How to determine what is the bottleneck in a PC-to-PC LAN connection?

Question

Computer networks

Initial data:
There are 100 Mbit cards in 2 computers (the computers are different, the performance is different, the cards are different).
There is a patch cord (3-5m).
This case is networked.
We start transferring files from one machine to another using Samba, while having an efficiency different from one.
Question:
How to determine what is the bottleneck? Because of what, specifically, the speed is cut?
PS I understand that the ideal is not achieved. But I’m not just asking the question, it would really be possible to have more speed, it seems to me.

Answer 1

Obviously samba.
Well, you can check that the problem is not in the network with iperf.

Answer 2

on gigabit, such a difference in speed is explained very simply - the speed of the HDD or the load on the CPU / data buses.
at 100 Mbps, the difference in speed is incomprehensible, if the hardware is weak, then it is explained by the fact that samba is a heavier application than ftp.
Check iron.

Answer 3

Because I can only guess about the level of your knowledge, then I dare to ask, but how is the cable crimped?

Answer 4

What is the result of copying and burning with iperf?
Accidentally not 11-12mb / s? :)

Answer 5

The answers have already been given, I'll add a few notes for better understanding.
First. Everyone writes: Samba is “guilty”. Not guilty, but just has a certain overhead. Both the protocol itself and its implementation. Windows also has these costs, but less (in the ideal case) due to years of polished implementation and great optimization opportunities for the OS. Of the Samba developers, no one aims to "catch up and overtake", since the protocol is not native.
Second. The SMB protocol is designed not at all for transferring large files, but for the operation of applications with them over the network. That is, reading / writing in small portions to different places in the file. Plus, sharing support brings its own requirements.
Third. You will not achieve 100% utilization in any way, it is foolish to expect this. Think about how many protocols there are in the TCP/IP stack and each one has some overhead.
Well, just a note. If you need to quickly transfer something huge over the network, there is nothing better than the good old nc. Zero overhead at the application layer. Just don't forget to check the checksums (md5sum) afterwards.